Nefarious individuals attempt to compromise computer systems in a variety of ways. As an example, such individuals may embed or otherwise include malicious software (“malware”) in email attachments and transmit or cause them to be transmitted to unsuspecting users. An administrator of the recipient computer system can attempt to prevent compromise by blocking all downloads of all attachments by the computer system. However, such a policy will also prevent legitimate attachments from being available to the user. As an alternate approach, the administrator can require that a security scan be performed prior to the download of an attachment. Unfortunately, malware authors are crafting increasingly sophisticated malware that is increasingly able to evade detection. Accordingly, there exists an ongoing need for improved techniques to detect malware and prevent its harm.